The way I understand the OS Inhibitor is that it stalls the development of the issues in the OS. This makes the OS feel as though it has slowed down to the audience, but it doesn't necessarily mean that anything has actually slowed down from the perspective of the characters.

Often the usage of the Inhibitor is explained as being able to slow down the OS, so that you can move to an exploration of another throughline. This way, when you go back to the OS, it makes sense that nothing has really advanced.

Even if the inhibitor does actually slow down time in the story world, this isn't necessarily an advantage to the antagonist (maybe in a timelock). Sometimes the characters need that time to work things out.

Consider also that the Inhibitor isn't connected to the Outcome (as far as I know), while the antagonist wants Failure.

I checked in the software just to verify this statement. It turns out this isn't strictly true. After you pick a Goal/ OS Concern, you have 8 possible elements to choose as OS Inhibitors; they'll be the 4 Issues under the Concern in the Domain dynamically opposed to the OS, and the 4 in the Domain to the right or left of the OS. If you then pick both an Outcome and a Judgment, you'll lose 1 option for OS Inhibitor from each Concern, leaving 6. Each of the four combinations of Outcome/ Judgment removes a different pair of choices.

I'm not sure what that really means. Everything in Dramatica is connected to a bunch of other things in the sense that every choice you make limits the available choices in other areas of the storyform. I'm not sure this should be taken to mean that these things are always related to one another in a sense that we can easily define.

Consider that in Failure stories, the RS Throughline shares the same problem element as the OS. In these stories the antagonist wins, but we don't reckon there's a connection between the RS and the antagonist, or that the RS is somehow an advantage to the antagonist. We might tell the story in such a way that the antagonist leverages the RS to achieve victory, but it's not required; it's an authorial choice. Likewise, you could tell a story in which OS Inhibitor works in the antagonist's favor, but that's a storytelling choice. It's not baked into Dramatica.